(1) Field of the Invention
The present invention relates to a shock absorber controller for altering a damping force of a shock absorber in a vehicle suspension in response to a vertical movement of a vehicle body due to a rough road surface.
(2) Description of the Prior Art
Conventionally, there is known an apparatus for controlling a damping force of a shock absorber provided between a vehicle body and each wheel so that a vertical movement of a vehicle body due to a rough road surface is suppressed in an early stage of the vertical movement. Japanese Laid-Open Patent Application No. 62-166104, entitled "SHOCK ABSORBER CONTROLLER", discloses an apparatus in which the shock absorber is controlled so that the damping force thereof is altered from a weak state to a strong state when a predetermined delay time has elapsed after the vehicle height exceeds to a definite value. The predetermined delay time is determined, taking into consideration the vertical movement cycle of the vehicle body so that the magnitude of the damping force is changed within half of the first one-cycle of the vertical movement. With this arrangement, it is possible to suppress a large vertical vehicle movement within half of the first one-cycle so that the vehicle height can return to a mean vehicle height or position.
The increased damping force of the shock absorber must be decreased to the weak state when the vertical movement of the vehicle body is considerably suppressed. For example, the damping force is maintained in the strong state for a predetermined hold time and is then returned to the weak state.
However, the above-mentioned prior shock absorber controller has the following disadvantages. In actuality, it is very difficult to suppress a vertical movement of the vehicle body by means of an increased damping force. For example, there is a possibility that the vehicle height may exceed the aforementioned definite value again even during the predetermined hold time. In this case, an instruction is generated again which causes the damping force of the shock absorber to be increased to the strong state after the predetermined delay time from the time when the vehicle height exceeds the definite value again. In this case, the hold time is renewed so that the damping force of the shock absorber may be maintained in the strong state for a longer time than necessary. That is, it is determined that the vehicle is running on a continuous rough road even when the road surface is smooth, and thus the damping force is maintained in the strong state. This deteriorates ride comfort.